The invention relates to systems and devices for measuring concentrations of nanometer or ultrafine particles, and more particularly to such systems that are adjustable in terms of their sensitivities to certain sizes or electrical mobilities of particles or sets of particles that fall within the nanometer size range.
When materials are produced or formed in the nanometer size range, i.e. from about 1 micrometer in diameter down to molecular levels, they exhibit unique properties that influence their physical, chemical and biological behavior. Nanotechnology, the field of endeavor concerned with materials in this size range, has experienced explosive growth over the last several years as new and diverse uses for nanomaterials are discovered and developed throughout a broad range of industries.
These developments have raised concerns, because the occupational health risks associated with manufacturing and using nanomaterials are not clearly understood. Many nanomaterials are formed from nanoparticles initially produced as aerosols or colloidal suspensions. Workers may be exposed to these particles through inhalation, dermal contact and ingestion, at increased levels due to working environments with nanoparticles in concentrations that far exceed ambient levels.
Traditionally, health related concerns about airborne particles have focused on particle concentrations in terms of mass per unit volume. Under this approach, permitted maximum concentration standards are determined, and mass concentrations are measured with respect to these standards. However, toxicologic studies involving ultrafine particles (0.1 micron diameter and below) suggest that particle surface area, as compared to particle mass, is the better indicator of health effects. This may follow from the fact that for any given shape (e.g. spherical), the smaller the particle, the greater is its surface area compared to its volume or mass. A proportionally larger specific surface area (i.e. surface area divided by mass) increases the tendency of a particle to react with chemicals in the body. Moreover, due to the small mass of nanoparticles, mass concentration measurements are difficult to obtain and lack the requisite sensitivity, even when based on particle accumulation such as through collection of particles on a filter. Additional studies have also suggested that health effects may also be correlated with the number of inhaled ultrafine particles that impact the lungs. Accordingly, instruments that measure particle concentrations in terms of surface area and particle number in the nanometer size range are expected to provide more useful assessments of health risks due to nanoparticle exposure.